This invention relates to a rotary and a method for facilitating the connection of pipes, and more particularly, but not exclusively, to a rotary for a powered drill pipe tong for facilitating the connection of sections or stands of drill pipe to a string of drill pipe.
Drill pipe tongs are commonly used for facilitating the connection of sections or stands of drill pipe to a pipe string. Typically, the pipe string hangs in a wellbore from a spider in a floor of an oil or gas rig.
A section or stand of drill pipe to be connected to the pipe string is swung in from a drill pipe rack to the well centre above the pipe string. A pipe handling arm may be used to guide the drill pipe to a position above the pipe string. A stabbing guide may then be used to align a threaded pin of the drill pipe with a threaded box of the pipe string. A drill pipe tong is then used to tighten the connection to a torque of typically 68,000 Nm (50,000 lb.ft)
The drill pipe tong is also used for disconnecting drill pipe. This operation involves breaking the connection which requires a torque typically greater than the tightening torque which may typically be in the order of 110,000 Nm (80,000 lb.ft).
A drill pipe tong generally comprises jaws mounted in a rotary which is rotatably arranged in a housing. The jaws are moveable relative to the rotary in a generally radial direction towards and away from an upset part of the pipe to be gripped. The upset parts of the pipe are generally located above the pin and below the box of the pipe and have an enlarged outer diameter and/or a reduced inner diameter.
In use, the rotary is rotated forcing the jaws along cam surfaces towards the upset part of the section of pipe. Once the jaws fully engage the upset part, the rotary carries on rotating applying torque to the threads and hence tightens the connection between the section of pipe and the pipe string.
Several problems have been observed with such prior art drill pipe tongs.
In particular, such drill pipe tongs can badly scar the upset part of the pipe, particularly if the jaws start rotating relative to the drill pipe.
Once scarred, the pipe is then lowered into the wellbore. Friction between the wellbore (or casing lining the wellbore) and the scarred upset grinds the upset, reducing the diameter.
Scarring of the upset may also be caused by having to reapply the jaws. This is especially common when connecting pipe with xe2x80x9cwedge threadsxe2x80x9d which requires approximately 80xc2x0 of turn in order to toque the connection. Many prior art wrenching tongs need to be reapplied to the pipe every 25xc2x0.
A reduction in diameter of the upset requires the use of a new drill pipe tong or for the old drill pipe tong to be modified therefor.
An attempt at solving this problem is disclosed in PCT Publication Number WO 92/18744, which discloses a rotary comprising hydraulically operated active jaws and stationary passive jaws. The hydraulically activated jaws are engaged fully with the pipe prior to rotation of the rotary, thereby substantially reducing scarring. A hydraulic circuit is provided on the rotary for actuating the jaws. A plunger is used to activate the hydraulic system by depressing a hydraulic piston of the hydraulic circuit repeatedly. This operation takes time. If several seconds can be saved per connection, the overall cost of the construction of an oil or gas well can be drastically reduced, as long as reliability is not sacrificed.
Another problem associated with the rotary disclosed in PCT Publication Number WO 92/18744 is that repeated depressing of the plunger for engaging the jaws fully with the pipe may itself cause some scaring.
According to a first aspect of the invention, there is provided a rotary comprising at least one jaw and means for displacing said at least one jaw, characterised in that said means is actuable by or connectable to pneumatic fluid.
Preferably, said pneumatic fluid is supplied from a supply external to said rotary.
Advantageously, said supply is connectable to said rotor by a coupling.
Preferably, said at least one jaw is displaceable on a piston.
Advantageously, said means for displacing said at least one jaw comprises a hydraulic circuit.
Preferably, said hydraulic circuit comprises a hydraulic pump driven by said pneumatic fluid.
Advantageously, said hydraulic circuit comprises a bellows which, in use may be used to pressurise said hydraulic circuit.
Preferably, said hydraulic circuit comprises an accumulator, which in use, is used to displace said at least one jaw.
Advantageously, said rotary comprises three jaws, all of which are displaceable by said means.
There is also provided a method for facilitating the connection of pipes using the rotary of the first aspect of the invention, the method comprising the step of applying pneumatic fluid to said means to displace said at least one jaw.
According to a second aspect of the invention, there is provided a rotary comprising at least one jaw and hydraulic fluid in a hydraulic circuit for displacing said at least one jaw, characterised in that said rotary comprises a pump for pumping said hydraulic fluid through said hydraulic circuit.
Preferably, said at least one jaw is displaceable on a piston.
Advantageously, said pump is drivable by a pneumatic fluid.
Preferably, said rotary further comprises an accumulator, which in use is charged by said hydraulic pump for displacing said at least one jaw. The accumulator may be used for disengaging the at least one jaw from a pipe and/or for engaging the at least one jaw with a pipe.
There is also provided a method for facilitating the connection of pipes using the rotary of the second aspect of the invention, the method comprising the step of pumping hydraulic fluid through said hydraulic circuit to displace said at least one jaw.
The rotary disclosed in PCT Publication Number WO 92/18744 comprises an accumulator for maintaining full engagement of said jaws with a pipe in case of any leaks or movement of the jaws. A similar device is used in the specific embodiment of the present invention, but is referred to as a bellows.
According to a third aspect of the invention, there is provided a rotary comprising at least one jaw and means for displacing said jaw characterised in that said rotary comprises an accumulator for storing a charge for displacing said jaw. The accumulator may be used to displace said at least one jaw for disengaging a pipe or engaging a pipe. The accumulator may comprise a hydraulic accumulator or any other form of energy storage device, for example a spring or an electrical accumulator (not recommended).
Preferably, said at least one jaw is displaceable on a piston.
Advantageously, said means for displacing said jaws comprises a hydraulic circuit.
Preferably, said hydraulic circuit comprises a pump for charging said accumulator.
Advantageously, said pump is drivable by said pneumatic fluid.
Preferably, said accumulator is provided with a check valve arranged in series, such that said accumulator may be charged therethrough inhibiting said is accumulator discharging.
Advantageously, said accumulator is provided with a release valve arranged in series therewith, such that upon actuation of said release valve said charge discharges from said accumulator to displace said at least one jaw.
Preferably, said release valve is provided with at least a second release valve arranged in parallel therewith.
There is also provided a method for facilitating the connection of pipes using the rotary of the third aspect of the invention, the method comprising the step of charging said accumulator and using said charge to displace said at least one jaw.
Another problem associated with the rotary disclosed in PCT Publication Number WO 92/18744 is that disengagement of the jaws is carried out by relieving the pressure of the hydraulic fluid in the hydraulic circuit and moving the jaws from engagement with a pipe manually.
According to a forth aspect of the invention there is provided a rotary comprising at least one jaw and means for moving said jaw into engagement with a pipe, characterised in that there is also provided power operable retracting means for retracting said at least one jaw.
Preferably, said at least one jaw is displaceable on a piston.
Advantageously, said retracting means comprises an accumulator.
Preferably, said means for displacing said at least one jaw comprises a hydraulic circuit.
Advantageously, said hydraulic circuit comprises a pump for charging said accumulator.
Preferably, the accumulator is located in said rotary.
There is also provided a method for facilitating the connection of pipes using the rotary of the forth aspect of the invention, the method comprising the step of operating said disengagement means for disengaging said at least one jaw from a pipe.
Another problem associated with the rotary disclosed in PCT Publication Number WO 92/18744 is that the hydraulic circuit arranged on the rotary comprises a reservoir which is open to the ambient air and may allow hydraulic fluid to leak therefrom.
According to a fifth aspect of the invention there is provided a rotary comprising at least one jaw and hydraulic fluid in a hydraulic circuit for displacing said jaw characterised in that said hydraulic circuit is sealed. No hydraulic fluid is open to air.
Preferably, said hydraulic circuit comprises a bellows for containing hydraulic fluid.